const defaultState={
    inputValue:'hello',
    list:[1,2,3]
};
/* state指store中的数据 */
/* reducer可以接收state,但不能修改state */
export default (state=defaultState,action)=>{
    /* ruducer拿到之前的数据,和action中传递过来的数据作比对 */
    if(action.type==='change_input_value'){
        const newState = {...state};
        newState.inputValue = action.value;
        return newState;
    }
    if(action.type==="add_todo_item"){
        const newState ={...state};
        newState.list.push(newState.inputValue)
        newState.inputValue=""
        return newState
    }
    if(action.type==="delete_item"){
        const newState = {...state};
        newState.list.splice(action.index,1);
        return newState;
    }
    return state;
    
}